Scientists have uncovered key attributes of so-called "brown carbon" from wildfires, airborne atmospheric particles that may have influenced current climate models that failed to take the material's warming effects into account. The work was described by a collaborative team of researchers from Los Alamos National Laboratory, Carnegie Mellon University and the University of Montana in the journal Nature Geosciences.

"Biomass burning and wildfires emit fine particulates that are toxic to humans and can warm or cool climate. While their toxicity is certain, their specific climatic effects remain unclear and are a hot research topic," said Manvendra Dubey, a senior Los Alamos climate scientist. "Smoke from wildfires accounts for one-third of Earth's 'black' carbon -- the familiar charred particles that are associated with fires with large flames. While black carbon is relatively simple -- solely consisting of carbon -- brown carbon contains a complex soup of organicmaterial, making it difficult to identify, characterize and model."

Black carbon or soot that absorbs sunlight at all wavelengths is a well-known, potent warmer. Its twin, organiccarbon co-emitted by fires, reflects sunlight and so can cool the climate. These two opposing effects cancel each other out, causing current climate models to predict that wildfires have a small net effect on climate. However, there is a third form of emission, called brown carbon, that absorbs sunlight at short blue wavelengths that is also in the soup of fire emissions.

The study discovered that brown carbon shares a common production mechanism with black carbon. Brown carbon's opticalproperties and volatility are highly variable and complex and no systematic treatment has been feasible in current models. In fact "what makes matters worse is many models treat brown carbon as organiccarbon, a double whammy since they are computing a cooling effect for what is actually a warming particle," said Dubey. Clearly, he said, models could be significantly under-estimating warming effect of fires both now and in the future.

"You might call brown carbon frustrated black carbon that is made when the wood isn't fully cooked all the way," said Dubey. Brown carbon warms the atmosphere similarly to black carbon, but the actual prevalence of brown carbon in wildfire smoke has been a large question mark. This study should answer this by providing a simple treatment of all absorbing fire particles in models and improve climate predictions.

The Los Alamos team of Dubey, Allison Aiken and Shang Liu performed controlled laboratory experiments of the opticalproperties of particles emitted by globally important fuels. They carefully manipulated the particles by heating to remove the volatile components and then monitored changes in opticalproperties. Analysis revealed that the least volatile fraction, that is most likely to be transported globally similar to refractory black carbon, is much more light absorbing than the volatile fraction.

This finding clearly establishes the "global significance of brown carbonaerosol, a research area prioritized by DOE's AtmosphericSystem Research (ASR) program, and our discovery shows how this missing warming agent can be effectively treated in DOE's climate models" said Dubey.

The three-institution research team included both experimentalists and modelers who understand each other's languages and the experimentalists, know what the modelers need, and had this in mind for the experimental design, noted Rawad Saleh, a postdoctoral researcher at Carnegie Mellon and one of the leads on the study.

Feedback

Tell us what you think of Chemistry 2011 -- we welcome both positive and negative comments. Have any problems using the site? Questions?

Your Name:Your Email:Comments:Click button to submit feedback:

About us

Chemistry2011 is an informational resource for students, educators and the self-taught in the field of chemistry. We offer resources such as course materials, chemistry department listings, activities, events, projects and more along with current news releases.

The history of the domain extends back to 2008 when it was selected to be used as the host domain for the International Year of Chemistry 2011 as designated by UNESCO and as an initiative of IUPAC that celebrated the achievements of chemistry. You can learn more about IYC2011 by clicking here. With IYC 2011 now over, the domain is currently under redevelopment by The Equipment Leasing Company Ltd.

Events & Activities

Are you interested in listing an event or sharing an activity or idea? Perhaps you are coordinating an event and are in need of additional resources?
Within our site you will find a variety of activities and projects your peers have previously submitted or which have been freely shared through creative commons licenses.
Here are some highlights: Featured Idea 1, Featured Idea 2.

About you

Ready to get involved? The first step is to sign up by following the link: Join Here. Also don’t forget to fill out your profile including any professional designations.